A snow retaining gate for a snow plow, of the general type to which this invention relates, was disclosed in U.S. Pat. No. 3,407,519. As was conventional, the horizontally elongated blade of the plow of that patent extended lengthwise obliquely to the normal direction of travel of the vehicle that carried it, so that one end of the blade trailed the other relative to that direction of travel. As such a plow blade moves forward during plowing, snow displaced by the blade slides lengthwise along it to its trailing end and then normally continues on out beyond that end to form a snow bank bordering the swath that the blade has plowed. Such a snow bank is of course objectionable when it is thrown across a driveway or cross-walk that intersects the plowed street or road. Therefore, to prevent formation of a snow bank when the plow crossed a driveway or the like, the snow plow of the patent had a snow retaining gate swingably mounted in front of its blade, near the trailing end thereof. For normal plowing, the gate was maintained in a raised inoperative position in which it was substantially horizontal and was out of the way of snow moving along the lower portion of the blade. When the plow was to cross a driveway or the like, the gate was lowered to an operative position in which it was substantially vertical and extended forwardly from the blade so that it lay across the path of snow moving along the blade and prevented such snow from flowing out beyond the trailing end of the blade and forming a snow bank.
In the snow plow of that patent, the gate swung about a shaft that projected forwardly from the plow blade at a level about midway between the top and bottom edges of the blade. The gate was connected to the shaft by means of an arm that projected laterally from the shaft, and in both positions of the gate its upper edge extended substantially parallel to the shaft axis. So that the gate could be swung to its inoperative position without interference from the forwardly curved upper portion of the plow blade, the height of the gate, as measured in its operative position, was only about half that of the blade; and therefore if any substantial accumulation of snow was being retained by the gate, a substantial portion of that snow would flow over its relatively low top edge, forming a snow bank such as the gate was intended to prevent.
Another prior snow retaining gate arrangement for a snow plow is disclosed in Swedish Pat. No. 7401343-4, published Sept. 13, 1976. When the snow retaining gate of that patent was in its lowered operative position, it extended forwardly from the plow blade at an oblique angle to the direction of travel such that its front edge projected laterally beyond its rear edge. That orientation of the snow retaining gate at an outwardly oblique angle to the direction of travel had the same major disadvantage as the insufficiently high gate of the U.S. patent, that is, it permitted formation of a secondary snow strand or snow bank across a driveway or cross-walk that was intended to be kept clear, especially during plowing of very deep snow or when a relatively wide driveway or the like was to be crossed by the plow. In this case, however, the secondary snow bank was formed by snow flowing out around the front edge of the gate.
The general object of the present invention is to provide a snow plow having a snow retaining gate which is substantially more effective when in its operative position than prior such devices and which, in particular, does not permit a secondary snow bank to develop even when a substantially large quantity of snow accumulates near the discharge end of the plow blade.
Another object of this invention is to provide a snow retaining gate of the character described that is sturdy in itself and does not impose any unduly high forces upon the structure by which it is carried.